Doctor blade device

ABSTRACT

A doctor blade device ( 01 ) for cleaning a surface has a doctor blade ( 03 ) and a tub ( 09 ) for receiving the material stripped from the surface by the doctor blade. The doctor blade is movable between a position in which it projects out of an opening ( 13 ) of the tub and a position in which it is submerged in the tub. A closure element ( 07 ) closes the opening in the submerged position of the doctor blade.

The present invention relates to a doctor blade device according to theprecharacterizing clause of claim 1.

Washing apparatuses are known for the automatic cleaning of ink-carryingrolls in a printing press, which washing apparatuses comprise spraynozzles or similar means for applying a cleaning fluid to the surfacewhich is to be cleaned, and also comprise a doctor blade device whichserves for pressing a flexible doctor blade against the surface which iswetted with the washing fluid, and thus for wiping off the washing fluidtogether with ink which is dissolved in it. The ink solution which isobtained in this way runs off into a trough of the doctor blade deviceand is led away via the latter. After the end of the washing process,ink residues remain on a conventional doctor blade device of this type,which ink residues have to be removed by hand, as they would otherwisedry on the doctor blade and damage the surface of the roll to be cleanedwhen said doctor blade is used again.

The invention is based on the aim of providing a doctor blade device.

According to the invention, the object is achieved by the features ofclaim 1.

The advantages which can be attained with the invention consist, inparticular, in the fact that it is possible to avoid ink drying andsolidifying on the doctor blade when the latter is not in use, as aconsequence of the capability to lower the doctor blade into the troughand to close the trough.

As the trough in general has an elongate shape with a slot-shapedopening for the emerging doctor blade, a possibility for closing thetrough can be provided in a simple manner by the trough being configuredin the shape of a cylindrical chamber, about the axis of which theclosure element can rotate between an open and a closed position. Here,the closure element is preferably arranged within the chamber.

The movement of the doctor blade between the position which protrudesout of the trough and the lowered position is preferably a pivotingmovement, and an actuator for driving this pivoting movement is providedon the doctor blade device.

The doctor blade is preferably deformed elastically in the loweredposition.

A particularly simple construction results if the closure element can bepivoted by the same actuator which also drives the movement of thedoctor blade between the position which protrudes out of the trough andthe lowered position.

In order not only to prevent the drying of wiped off ink on the doctorblade but also, moreover, for it to be possible for wiped off inkresidues to be removed automatically from the doctor blade, it isdesirable for the trough to be provided with a feed line and a dischargeline for a cleaning fluid. In the closed state of the trough, thecleaning fluid can be pumped through said trough at a high flow speed,in order to release and rinse away ink residues over time which adheretenaciously to the doctor blade.

In order to attain an effective flow through the chamber, it isdesirable for the feed line and the discharge line to open into in eachcase opposite ends of the trough.

The doctor blade device preferably also comprises a pump for circulatingcleaning fluid through the trough. Expediently, this pump can beassigned a control apparatus which is coupled to the position of theclosure element and, when the chamber is closed, permits a higherthroughput of the pump than when the chamber is open. It is appropriateto allow a flow of cleaning fluid when the chamber is open, even if saidflow is weak, in order continuously to rinse off ink residues which thedoctor blade wipes off from the roll surface which is to be cleanedduring operation of the doctor blade device. The throughflow rate whenthe chamber is open has to be selected to be low enough that cleaningfluid does not spray out of the opening of the chamber. In contrast,when the chamber is closed, substantially higher throughflow rates canbe used advantageously for the cleaning fluid.

It is desirable for ecological and economical reasons for the cleaningfluid to circulate in a closed circuit. This circuit expediently has atleast one filter element for separating ink residues out of the flow ofthe cleaning fluid.

Exemplary embodiments of the invention are shown in the drawings andwill be described in greater detail in the following text.

In the figures:

FIG. 1 shows a diagrammatic section through a first refinement of adoctor blade device, in which the doctor blade is extended out of thechamber;

FIG. 2 shows a diagrammatic section through the doctor blade device fromFIG. 1, in which the doctor blade is lowered into the trough;

FIG. 3 shows an axial section along the line III-III from FIG. 1;

FIG. 4 shows a section, which is analogous to that of FIG. 1, through asecond embodiment of the doctor blade device;

FIG. 5 shows a section through the doctor blade device according to asecond embodiment, with a lowered doctor blade; and

FIG. 6 shows a block diagram of the doctor blade device.

FIG. 1 shows a diagrammatic section through a doctor blade device 01with a doctor blade 03 which is set against an inking roll 02 of aprinting press. The inking roll 02 is shown only as a detail, over aquarter of its circumference.

The doctor blade 03 is a strip which extends at least over the activeaxial width of the inking roll 02 and is composed of a flexible plasticor rubber material. In the extended position of the doctor blade 03which is shown in FIG. 1, one longitudinal edge 04 of the doctor blade03 is in contact with the surface of the inking roll 02.

An opposite longitudinal edge 06 of the doctor blade 03 is clamped in aclosure element 07 in the shape of a cylinder sector, for example aholding element 07. The holding element 07 is accommodated rotatably ina cylindrical chamber 08 of a trough 09. As shown in FIG. 3, the trough09 is composed of two end plates 11 which lie opposite one another and acover 12 which connects the two end plates 11. The cover 12 hassubstantially the shape of a cylinder, with an elongate opening 13, forexample a slot 13, on its upper side and an elongate tongue 14 which isbent outward at one end of the slot 13 and serves as a support 14 forthe doctor blade 03 when the inking roll 02 is being wiped.

Both end plates 11 are provided with a hole 16, to which in each case afeed line or discharge line 17 for a cleaning fluid is connected.

When the inking roll 02 is being cleaned, a nozzle rail (not shown)sprays a cleaning fluid onto the entire width of the cover of the inkingroll 02. The inking roll 02 rotates in the counterclockwise direction inrelation to FIG. 1. The doctor blade 03 presses against the surface ofthe inking roll 02 at an acute angle. The friction which occurs hereincreases the pressure between the doctor blade 03 and the inking roll02 and, moreover, presses the doctor blade 03 against the supportingtongue 14 of the trough 09. A mixture of cleaning fluid and ink residueswhich is moved over the surface of the inking roll 02 is wiped off bythe doctor blade 03 and flows downward on the latter into the trough 09,where it is entrained by a flow of cleaning fluid which flows throughthe trough 09 in the longitudinal direction from the feed line to thedischarge line 17. The throughput of the cleaning fluid in this state ismeasured to be just sufficient to ensure that the ink residues arerinsed away reliably and are not deposited in the trough 09. For thispurpose, it is not necessary for the flow to fill the entire crosssection of the trough 09.

After the inking roll 02 has been cleaned, the holding element 07together with the doctor blade 03 is rotated about the longitudinal axisA of the chamber 08 into the position which is shown in FIG. 2. For thispurpose, the holding element 07 merges at its two longitudinal ends intoa cylindrical ring 18 which is closed in the circumferential directionand fills the inner cross section of the likewise cylindrical chamber 08exactly. An external toothing system 19 which meshes with a pinion 21 isformed on each of these rings 18. The pinions 21 at both ends of thetrough 09 are driven by an identical actuating motor (not shown). Theexternal toothing systems 19 are protected in each case by sealing rings22 against the infiltration of rinsing fluid and possibly ink.

FIG. 2 shows the doctor blade device 01 in a configuration, in which theholding element 07 with the doctor blade 03 is rotated in the clockwisedirection by not quite 180° compared with the configuration of FIG. 1.Here, the doctor blade 03 is situated in a position which is withdrawncompletely into the chamber 08. Instead of against the inking roll 02,the longitudinal edge 04 of the doctor blade 03 presses against thecover 12 of the trough 09, and the doctor blade 03 is bent elasticallyinto itself. The holding element 07 blocks the slot 13, with the resultthat the holding element 07 and the cover 12 form a tube which is closedall around. In order to clean the doctor blade 03, cleaning fluid ispumped at high speed through the chamber 08 in this configuration of thedoctor blade device 01. In contrast to the configuration of FIG. 1,where a uniform, laminar flow is required to prevent cleaning fluid fromspraying out of the trough 09, a turbulent flow can be accepted here andis even desirable, in order to improve the cleaning action on the doctorblade 03. The flow through the chamber 08 can be maintained for as longas is necessary to clean the doctor blade 03 with a desired accuracy.

As can be seen in the cross section in FIG. 2, the withdrawn doctorblade 03 separates a small region 23 of the cross section of the chamber08, which small region 23 does not communicate directly with the holes16 on the end plates 11 of the trough 09 and in which small region 23 nosignificant flow of the cleaning fluid therefore occurs. However, thisis insignificant for the efficacy of the cleaning of the doctor blade,as that lateral face of the doctor blade 03 which delimits the region 23is not reached by the ink/cleaning fluid mixture when the mixture isbeing wiped off the inking roll 02 and remains clean. If it should provenecessary in an individual case also to clean that surface of the doctorblade 03 which faces the region 23, it is not a problem to generate aflow of cleaning fluid in this region also, for example by the positionat least of the hole 16 which is connected to the feed line in its endplate 11 being displaced in such a way that at least part of its crosssection opens into the region 23.

FIG. 4 shows a second embodiment of a doctor blade device 01 in anillustration which is analogous to FIG. 1. Identical elements which arepresent in both embodiments are denoted by identical designations andwill not be described again. The doctor blade device 01 from FIG. 4 isdesigned for an inking roll 02 which rotates in the clockwise directionin the perspective of this figure. The doctor blade 03 is composed of arigid doctor blade lip 24 made from plastic and a spring 26, for examplea leaf spring 26 which, like the doctor blade lip 24, extends over theentire width of the inking roll 02. The leaf spring 26 is screwed on oneside to the doctor blade lip 24 and on the other side to a holdingelement 07 which has the same functions as the holding element 07 fromFIG. 1. The tongue 14 of the embodiment from FIG. 1 is replaced by arail 27 which is screwed to the cover 12 and holds the free longitudinaledge 04 of the doctor blade 03 pressed against the inking roll 02. Therail 27 can be removed, in order to gain access to the interior of thetrough 09 for maintenance and repair purposes.

The feed and discharge lines 17 for cleaning fluid are not guidedthrough the end plates 11, but through the cover 12 of the trough 09near the ends which lie opposite one another.

If the doctor blade 03 is situated in the withdrawn position which isshown in FIG. 5, it divides the free inner space of the chamber 08 intotwo regions 23, 28. The feed line 17 is arranged in such a way that itopens into the region 23 which is delimited by that lateral side of thedoctor blade 03 which bears wiped-off ink in this embodiment. Thedischarge line 17 opens into the region 28. A flow of cleaning fluidwhich is pumped through the chamber 08 via the feed and discharge lines17 rinses the chamber 08 not only in the longitudinal direction, but italso displaces the doctor blade 03 a little away from the cover 12 backinto the interior of the chamber 08, with the result that a narrow gapis produced along the longitudinal edge 04 of the doctor blade 03,through which narrow gap the cleaning fluid moves at high speed from theregion 23 into the region 28. In this way, highly effective cleaning isattained, above all of the longitudinal edge 04 which is provided forcontact with the inking roll 02.

Two sealing strips 29 made from rubber are let into the body of theholding element 07 and rotate with the latter. They are placed in such away that, in the closed configuration which is shown in FIG. 5, theycome to rest on both sides of the slot 13 and prevent egress of thecleaning fluid toward the inking roll 02 reliably.

As the block diagram from FIG. 6 shows, the doctor blade device 01 alsocomprises a pump 30 which circulates the cleaning fluid in a closedcircuit. The pump 30 is coupled to a control circuit 32 which alsodrives the actuating motor 33 for the pivoting movement of the holdingelement 07 and the doctor blade 03. Coupled to the respective positionof the holding element 07, the control circuit 32 regulates thethroughput of cleaning fluid to a low value in the open position and toa high value which favors a turbulent flow of cleaning fluid in theclosed position. Furthermore, filters 31 for trapping ink residues whichare dissolved in the cleaning fluid are arranged in the closed circuit,with the result that the doctor blade device 01 can be operated for along time without maintenance.

1. A doctor blade device for cleaning a surface, having a doctor bladeand a trough for receiving material which is wiped off from the surfaceby the doctor blade, wherein the doctor blade can be moved between aposition in which it protrudes from an opening in the trough and aposition in which it is lowered into the trough, and wherein the troughhas a closure element which, in the lowered position of the doctorblade, is capable of closing the opening.
 2. The doctor blade device asclaimed in claim 1, wherein the trough has a cylindrical chamber, abouta longitudinal axis of which the closure element can rotate.
 3. Thedoctor blade device as claimed in claim 2, wherein the closure elementis arranged within the chamber.
 4. The doctor blade device as claimed inclaim 2, comprising an actuator for pivoting the doctor blade about thelongitudinal axis of the chamber between the position which protrudesout of the trough and the lowered position.
 5. The doctor blade deviceas claimed in claim 4, wherein the doctor blade is deformed elasticallyin the lowered position.
 6. The doctor blade device as claimed in claim4, wherein the closure element can be pivoted by the actuator.
 7. Thedoctor blade device as claimed in claim 1, wherein the trough isprovided with a feed line and a discharge line for a cleaning fluid. 8.The doctor blade device as claimed in claim 7, wherein the feed line andthe discharge line open into opposite end sections of the trough.
 9. Thedoctor blade device as claimed in claim 7, comprising a pump forcirculating cleaning fluid through the trough.
 10. The doctor bladedevice as claimed in claim 9, wherein a control circuit for the pump,which is coupled to the position of the closure element and, when thechamber is closed, permits a higher throughput of the pump than when thechamber is open.
 11. The doctor blade device as claimed in claim 7,comprising a closed circuit for the cleaning fluid.